Why isn't there a Fast-Food franchise that sells exclusively healthy meals?

Healthy choices have started to become available at many fast-food and franchise restaurants, but I’m surprised that no one has come up with one that specializes in only healthy stuff that tastes good and is fast.

I could imagine combo meals that advertise how many points they’re worth on the various diets out there. The food would probably be a bit more expensive than the cheapest places out there, but I’d bet it could be made for reasonably cheap prices. I’m envisioning a restaurant where if someone did the Supersize Me experiment, they’d actually loose weight and come out healthier.

Would this work? or are Americans too addicted to unhealthy portion sizes and fat? Would you eat at a place like this regularly? Why/why not?